1. Field of the Invention
The present invention relates to a read/write transducer for hard disk drives with dual actuation stage and to the manufacturing process thereof.
2. Description of the Related Art
As is known, hard disk drives are the media most widely used for storing data in personal computers; consequently they are produced in very large volumes and the maximum data storage density increases year by year.
The structure of a known hard disk drive is shown in FIGS. 1-3.
The hard disk drive, designated as a whole by 1, comprises a group of hard disks 2 rotating jointly with and parallel to each other around a rotation axis A and carried by a supporting structure 4 mounted on ball bearings (not shown) and actuated by a synchronous motor (not shown), generally known as “spindle motor.”
The hard disk drive 1 further comprises a read/write device 6 for reading/writing the hard disks 2, comprising a supporting structure generally known as “E-block” 8 because of its E-like shape in side view (see FIG. 2), which is angularly mobile around an oscillation axis B parallel to the rotation axis A of the hard disks 2 and is provided with a plurality of arms 10 orthogonal to the oscillation axis B and each carrying one or two suspensions 12, each formed by a steel lamina cantilevered with respect to the corresponding arm 10.
At the end not fixed to the corresponding arm 10, each suspension 12 carries a joint, generally known as “gimbal” or “flexure” 14, also made of steel, holding in turn a read/write transducer generally known as “slider” 16 and arranged, in operating condition, facing onto a surface of a corresponding hard disk 2, as shown in FIG. 2.
As shown in greater detail in FIG. 3, each gimbal 14 is generally formed from the corresponding suspension 12 and is composed, for example, of a rectangular plate 14a cut around on three and a half sides starting from the suspension 12 itself and having a portion 14b connected to the suspension 12 and allowing flexure of the plate 14a under the weight of the slider 16, which is therefore able to perform rolling and pitching movements in order to follow the surface of the corresponding hard disk 2.
Each slider 16 is formed by a supporting body 20 having a generally parallelepipedal shape with typical dimensions 1×1.2×0.3 mm, made of ceramic material, generally an alloy of aluminum, titanium and carbon (Al—Ti—C), and carrying, on its front face, a read/write head 22 (magneto/resistive and inductive) which constitutes the proper reading and writing device. Electrical bonding wires, not shown, extend from the read/write head 22 along the corresponding gimbal 14 and the corresponding suspension 12 to a signal processing device (also not shown) fixed to the mother board of the personal computer or other apparatus in which the hard disk drive is installed.
In the hard disk drives 1 currently on the market, each of the sliders 16 is glued directly onto the corresponding gimbal 14 and the movement of the read/write device 6 across the hard disks 2 is achieved with a motor, generally known as “voice coil motor” 24 (FIG. 1), coupled to the E-block 8 to move it angularly around the oscillation axis B.
After having been subjected to all the surface finishing operations and having been fitted on the E-block 8, and before the final closing of the protective external casing in which the hard disk drive 1 is placed, control information is stored in each of the hard disks 2 in specific so-called pilot traces of specific so-called servo control sectors or servo sectors. During operation, this control information is then read by the sliders 16 and supplied to servo control devices (not shown) which process it to determine the position of the suspensions 12, and therefore of the sliders 16 integral with them, with respect to the corresponding hard disks 2, and to realize a closed loop control of the position of the sliders 16 so as to keep the reading heads 22 in an optimum reading position.
The market demand for a constant increase of the data storage density of hard disk drives 1 leads to an increasingly closer packing of the traces of the hard disks 2 and so the intrinsically poor precision of the voice coil motor 24 does not provide sufficient guarantees for the execution of the initial operation of writing the control information in the pilot traces of the servo sectors of the hard disks 2.
To overcome this inconvenience, an external precision actuation device is currently used, generally known as “spin-stand” 26 (schematically illustrated in FIG. 1), which moves the E-block 8 with micrometric precision, and therefore also the sliders 16 on the corresponding hard disks 2, by means of its own output control shaft 28 coupled to one of the suspensions 12 and provided with an optical encoder (not shown).
Recently, however, to obtain more precise and finer control of the position of the slides 16 with respect to the corresponding hard disks 2, it has been proposed to use a moving device with dual actuation stage, in which a first rougher actuation stage including the voice coil motor 24 which moves the assembly formed by the E-block 8, the suspensions 12, the gimbals 14 and the sliders 16 across the hard disks 2 during the track coarse search, while a second finer actuation stage includes a plurality of integrated microactuators 30 (one of which is shown in FIG. 3) each arranged between a corresponding slider 16 and a corresponding gimbal 14 and having the aim of carrying out a finer regulation of the position of the sliders 16 during the tracking.
An example of an embodiment of a rotary electrostatic microactuator 30 is described in the European patent application number 98830269.1, filed May 5, 1998 in the name of the applicant.
The introduction of a degree of freedom of movement between each slider 16 and the corresponding suspension 12 resulting from the introduction of a microactuator 30 means that, in order to be able to carry out the aforementioned initial operation of writing the control information in the pilot traces of the servo sectors of the hard disks 2 with the spin-stand 26, it is necessary to know, not only the position of the suspensions 12 with respect to the corresponding hard disks 2, but also the position of the sliders 16 with respect to the corresponding suspensions 12.
The determination of the position of a slider 16 with respect to the corresponding suspension 12 could, at least theoretically, be carried out indirectly by determining the position of the microactuator 30, to which the slider 16 is restrained, with respect to the corresponding suspension 12, on the basis of the driving signals supplied to the microactuator 30, or by measuring the capacitive coupling existing between the rotor and the stator of the microactuator 30, since this coupling is correlated to the position of the microactuator 30.
In practice, however, this solution is difficult to put into practice, as the precision of determination of the position of the slider 16 with respect to the suspension 12 which may be obtained with this solution has proven to be insufficient for the execution of the initial operation of writing the control information in the pilot traces of the servo sectors in high data storage density applications in which the distances between the traces of the hard disks 2 are extremely reduced.
In fact, in the hard disk drives 1 with a dual actuation stage moving device of the type described above, the slider 16 is restrained to the corresponding microactuator 30 by gluing and generally the positioning of the slider 16 with respect to the microactuator 30 obtained with this type of connection presents a rather high degree of uncertainty, which has a significant influence on the precision of determination of the position of the slider 16 with respect to the suspension 12, making it insufficient for applications with high data storage density.